The present invention is related to a procedure and a device for manufacturing a rod of a material presenting a cross-sectional composition gradient and, more particularly, to such a procedure and such a device that make it possible to manufacture a glass rod of which one characteristic, such as the refractive index, the optical density, the ionic conductivity, etc., presents a cross-sectional gradient of a predetermined profile, established by a cross-sectional variation of its composition.
Commonly used today are optical components such as lenses made of a glass that presents an axially symmetric refractive index gradient transversely to the axis of the lens. Also used are optical fibers that present such an index gradient. In order to make such optical components, the composition of the glass is altered transversely to the axis of the component to be obtained by different techniques such as ion exchange (see FR-A-2,504,515), impregnation by the so-called "sol-gel" technique (see U.S. Pat. No. 5,069,700), the use of glass compositions starting with powder (U.S. Pat. No. 4,883,522), the use of a selectively doped porous glass (U.S. Pat. No. 4,620,861), the joining by fusion of glass chips of varied compositions (U.S. Pat. No. 4,929,065), if not by other techniques such as the exposure to neutron radiation, the deposition of glass in a vapor phase (in particular, for optical fibers), etc.
The techniques used heretofore share the application of discontinuous, i.e., batch manufacturing processes, with the discontinuity involving down time which is detrimental from the point of view of productivity of the process and therefore also from the point of view of reducing production costs. Moreover, the known procedures do not allow making, at least economically, components with diameters greater than 1 or 2 cm. The index gradients obtained furthermore have proven to be of insufficient amplitude in certain applications and with an insufficiently controlled profile.
Therefore, the purpose of the present invention is to carry out a procedure and furnish a device that makes it possible to manufacture rods of a material that presents a cross-sectional composition gradient and, in particular, glass rods for making optical components with a cross-sectional composition gradient that do not present any of the disadvantages of the known procedures and devices mentioned above.